1. Field of the Invention
The present invention relates to a hydraulic pressure supply system of an automatic transmission for a vehicle. More particularly, the present invention relates to a hydraulic pressure supply system of an automatic transmission for a vehicle which prevents rise of motor RPM due to reduction of hydraulic pressure and improves fuel economy by supplying hydraulic pressure generated by both of a low-pressure hydraulic pump and a high-pressure hydraulic pump to a high pressure portion when shifting.
2. Description of Related Art
Recently, vehicle makers direct all their strength to improve fuel economy due to worldwide high oil prices and strengthening of exhaust gas regulations.
Improvement of fuel economy may be achieved by improving power delivery efficiency, and the improvement of the power delivery efficiency may be achieved by minimizing unnecessary power consumption of a hydraulic pump.
A recent automatic transmission is provided with a low-pressure hydraulic pump and a high-pressure hydraulic pump so as to improve fuel economy. Therefore, hydraulic pressure generated by the low-pressure hydraulic pump is supplied to a low pressure portion (i.e., a torque converter, a cooling device, and a lubrication device), and hydraulic pressure generated by the high-pressure hydraulic pump is supplied to a high pressure portion (i.e., friction members selectively operated when shifting).
In further detail, general hydraulic pressure of the automatic transmission is generated for the low pressure portion (i.e., generated by the low-pressure hydraulic pump), and hydraulic pressure demanded by the high pressure portion is generated by the high-pressure hydraulic pump and then is supplied to the high pressure portion.
Therefore, fuel economy may be improved by minimizing power consumption for driving the hydraulic pump, and noise and vibration may be reduced and durability may be improved by reducing load applied to the hydraulic pump.
However, according to a conventional hydraulic pressure supply system, hydraulic pressure generated only by the high-pressure hydraulic pump is supplied to the high pressure portion in shifting where much oil is necessary. Therefore, RPM of the hydraulic pump may be excessively increased in order to prevent pressure reduction at the high pressure portion.
In this case, driving loss of the hydraulic pump may occur and fuel economy may be deteriorated.
The above information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.